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Mensuration Test - 27

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Mensuration Test - 27
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  • Question 1
    1 / -0
    Choose the correct formula for surface area of a cylinder.
    Solution
    A cylinder comprises two circles and one rectangle as given in the figure
    The surface area of a circle is $$\pi r^2$$ where $$r$$ is the radius and the surface area of a rectangle is $$2\pi rh$$.
    $$\implies$$ Surface area of cylinder $$=2\times$$ area of the circular base $$+$$ area of the rectangle
    $$\Rightarrow $$ Surface area of cylinder $$=2\pi r^2+2\pi rh$$

  • Question 2
    1 / -0
    Find the height of a cylinder that has a diameter of $$10$$ feet and a surface area of $$\displaystyle 220{\  ft }^{ 2 }$$. Round your answer to the nearest whole number.
    (use $$\displaystyle \pi ={ 22 }/{ 7 }$$).
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$
    Here the cylinder has surface area $$A=220$$ ft$$^2$$ and diameter $$10$$ ft and therefore, the radius is half of the diameter that is$$r=5$$ ft.
    Thus,
    $$A=2πr(r+h)\\ \Rightarrow 220=2\times \frac { 22 }{ 7 } \times 5(5+h)\\ \Rightarrow 220=\frac { 44 }{ 7 } (25+5h)\\ \Rightarrow 220\times 7=1100+220h\\ \Rightarrow 1540-1100=220h\\ \Rightarrow 220h=440\\ \Rightarrow h=\frac { 440 }{ 220 } =2$$
    Hence, the height of the cylinder is $$2$$ ft.
  • Question 3
    1 / -0
    A cylindrical drum has its height 20 inches and curved surface area as $$\displaystyle 200{ in }^{ 2 }$$. Find  surface area of cylindrical drum.($$\displaystyle \pi ={ 22 }/{ 7 }$$)
    Solution

  • Question 4
    1 / -0
    Judah wants to make a cylindrical drum that will fit a bass with a height $$15 $$in. and a diameter of $$48$$ in. What is the surface area of the drum?
    Take $$\pi = 3.14$$
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here, diameter is $$48$$ in and therefore, the radius is half of diameter that is $$r=24$$ in and the height is $$h=15$$ in.

    Thus,

    $$A=2πr(r+h)=2\times 3.14\times 24(24+15)=150.72\times 39=5878.08$$

    Hence, the surface area of the cylindrical drum is $$5878.08$$ in$$^2$$.

  • Question 5
    1 / -0
    Find the total surface area of the cylinder. (Use $$\displaystyle \pi =3.14$$).

    Solution
    Given: $$r=6ft$$ and $$h=12ft$$
    The total surface area of a cylinder = $$\displaystyle 2\pi r\left( r+h \right) $$
    $$\displaystyle =2\times 3.14\times 6\left( 6+12 \right) $$
    $$\displaystyle =2\times 3.14\times 6\left( 18 \right) $$
    $$=\displaystyle 678.24{ ft }^{ 2 }$$

    So, option D is correct.
  • Question 6
    1 / -0
    The surface area of a cylindrical box is $$\displaystyle 132\ { mm }^{ 2 }$$ and its height is $$4 \ mm.$$ Find its radius.
    Solution
    Given: Cylindrical box has surface area $$A=132$$ $$mm^2$$ and height $$h=4\ mm$$

    We know surface area of cylinder is $$A=2πr(r+h)$$

    Thus, $$ 132=2\times \dfrac { 22 }{ 7 } \times r(r+4)$$

    $$ \Rightarrow 132=\dfrac { 44 }{ 7 } r(r+4)$$

    $$ \Rightarrow 132\times 7=44r(r+4)$$

    $$\Rightarrow 924=44r^{ 2 }+176r$$

    $$\Rightarrow 44r^{ 2 }+176r-924=0$$

    $$ \Rightarrow r^{ 2 }+4r-21=0$$

    $$ \Rightarrow r^{ 2 }+7r-3r-21=0$$

    $$ \Rightarrow r(r+7)-3(r+7)=0$$

    $$ \Rightarrow r+7=0,\quad r-3=0$$

    $$ \Rightarrow r=-7,\quad r=3$$

    Hence, the radius of the cylindrical box is $$3$$ mm.
  • Question 7
    1 / -0
    A skating board rocks back and forth on a wooden cylinder. The cylinder has a radius of 6 inches and a surface area is $$\displaystyle 590{ in }^{ 2 }$$. Find the height of the cylinder. ($$\displaystyle \pi =3.14$$).
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here the wooden cylinder has surface area $$A=590$$ in$$^2$$ and radius $$r=6$$ mm.

    Thus,

    $$A=2πr(r+h)\\ \Rightarrow 590=2\times \dfrac { 22 }{ 7 } \times 6(6+h)\\ \Rightarrow 590=\dfrac { 44 }{ 7 } (36+6h)\\ \Rightarrow 590\times 7=1584+264h\\ \Rightarrow 4130-1584=264h\\ \Rightarrow 264h=2546\\ \Rightarrow h=\dfrac { 2546 }{ 264 } =9.643$$

    Hence, the height of the wooden cylinder is $$9.65$$ in.

  • Question 8
    1 / -0
    David built a recycling cylindrical bin that is 12 feet long and its base is 56 feet radius. Find the surface area of the bin.
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here the cylindrical bin has radius $$r=56$$ ft and height $$h=12$$ ft.

    Thus,

    $$A=2πr(r+h)=2\times 3.14\times 56(56+12)=351.68\times 68=23936.24$$

    Hence, the surface area of the cylindrical bin is approximately equal to $$23936$$ ft$$^2$$.

  • Question 9
    1 / -0
    A gas cylinder has a diameter of $$14 $$m and height is  $$0.2$$m. Find its surface area. ($$\displaystyle \pi ={ 22 }/{ 7 }$$)
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$
    Here the gas cylinder has diameter $$14$$ m and therefore, the radius is half of diameter that is $$r=7$$ m and height $$h=0.2$$ m.
    Thus,
    $$A=2πr(r+h)=2 \times \dfrac {22}{7}\times 7(7+0.2)=316.512$$
    Hence, the surface area of the gas cylinder is $$316.512m^2$$.
  • Question 10
    1 / -0
    The curved surface area of a cylinder is $$\displaystyle 188.4\ { m }^{ 2 }$$. The height is $$12\ m$$. What is the radius? (use$$\displaystyle \pi =3.14$$).
    Solution
    Curved surface area of cylinder is $$A=2πrh$$

    Here, the curved surface area is $$A=188.4\ m^2$$ the height is $$h=12\ m$$.

    Thus,

    $$A=2πrh\\ \Rightarrow 188.4=2\times 3.14\times r\times 12\\ \Rightarrow 188.4=75.36r\\ \Rightarrow r=\dfrac { 188.4 }{ 75.36 } =2.5$$

    Hence, radius of the cylinder is $$2.5\ m$$
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